1. Field of the Invention
This invention relates to a production of oil and/or gas from subterranean wellbores, and more particularly to prepacked well screens for preventing production of sand and other fine solids during production of oil and gas.
When oil and gas wells are drilled through formations which generally are of an unconsolidated nature, the produced fluids can be expected to contain some particulate matter, generally referred to as "sand". It is undesirable to produce such particulate matter with the production fluids because of abrasion of production tubing, valves and other equipment used to produce the well. It is therefore necessary in such instances to avoid production of such sand and other particulate matter with the fluids.
2. The Prior Art
In the past, those skilled in the art have reduced the production of sand by "gravel packing" the well during completion operations. Such gravel packing includes providing on the production conduit or tubular work string a device including a slotted or ported cylindrically shaped member which prevents the passage of solid particles exceeding a predeterminable size. Such devices are incorporated where gravel packing is placed in the annular area between the production conduit or workstring and the casing of the well, or in the event of non-cased wells, the well bore wall, with the gravel being deposited longitudinally exteriorly of the slotted or ported cylindrical member.
Gravel packing of such wells has also been effected by means of incorporation onto the production or workstring of a prepacked well screen, wherein gravel, glass beads, bauxite, or other solid particulate is disposed between an outer member, such as stainless steel wire wrap screen, and an inner ported member, such that the device may be lowered into the well and positioned adjacent the production zone to thereby prevent the particulate matter produced with the production fluids from entering the interior of the conduit and being produced to the top of the well with the production fluids.
The prior art contains a number of references to well screens incorporating slotted, ported or wire-wrapped screen devices which have disposed therein particulate matter, such as glass beads, gravel and the like.
U.S. Pat. No. 4,917,183 describes a gravel pack screen having fluid permeable particulate solids surrounded by a mesh support.
U.S. Pat. No. 4,821,800 describes a filter assembly including a filtering medium supported between a perforated production pipe and an outer mesh screen.
U.S. Pat. No. 4,487,259 describes a prepacked well screen similar in some respects to those described above.
In each of the devices described above, the outer surface of the filtering medium is coextensive with the surface of the outer supporting means surrounding the filtering medium. Since flow capacity through the filtering medium is proportional to the surface area, the outer surface of the outer filtering medium is a limiting factor. In the device shown in U.S. Pat. No. 4,487,259, the flow capacity of the filtering medium is further restricted by the outer casing member.